Heat and Thermodynamics (Physics) Part-II

Total Questions: 41

1. An assertion and its reason is given below - [Uttarakhand P.C.S. (Pre) 2012]

Assertion (A): Salt is used for cooking the food at places on higher from sea level.

Reason (R): Temperature is low in higher places. Which one among these is right answer?

Correct Answer: (b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Solution:

At high altitudes the atmospheric pressure is low. So water will boil at a lower temperature because the boiling point of water is lower at high altitude. It takes longer to cook at higher altitudes than at sea level.

Adding a little salt to the water will cause the water to boil at a slightly higher temperature, which can be helpful while cooking especially at high altitudes. Lower pressure at higher altitudes causes the temperature to be colder.

2. To keep drinks at the same temperature for quite sometime, the walls of thermos bottle are coated with : [R.A.S./R.T.S. (Pre) 1996]

Correct Answer: (c) Silver layer
Solution:

The glass or steel which is used in thermos bottle is coated with a silver layer to keep drinks at the same temperature for some time.

3. It is more comfortable to wear white cloth in summer because [U.P.P.C.S. (Pre) 2007]

Correct Answer: (a) They reflect all the heat falling on them
Solution:

We use white clothes in summer because white clothes are good reflectors of heat. Thus, we do not feel warm. In winter, gray or dull coloured clothes are used because gray or dull coloured clothes are good absorbers of heat.

4. White clothes are cooler than black clothes because : [U.P.R.O/A.R.O. (Mains) 2016]

Correct Answer: (d) They reflect the whole light
Solution:

We use white clothes in summer because white clothes are good reflectors of heat. Thus, we do not feel warm. In winter, gray or dull coloured clothes are used because gray or dull coloured clothes are good absorbers of heat.

5. Assertion and Reason are given below - [Uttarakhand P.C.S. (Pre) 2012]

Assertion (A): We prefer the white dress in winters.

Reason (R): White dresses are good reflectors of heat.

Which one among these is the right answer.

Correct Answer: (d) (A) is false, but (R) is true.
Solution:

We use white clothes in summer because white clothes are good reflectors of heat. Thus, we do not feel warm. In winter, gray or dull coloured clothes are used because gray or dull coloured clothes are good absorbers of heat.

6. Consider the following statements : [U.P.R.O./A.R.O. (Pre) 2016]

Assertion (A): Light coloured clothes are preferred in summer.

Reason (R): Light colours are poor absorbers of heat.

Select correct answer from the code given below:

Correct Answer: (a) Both (A) and (R) are correct and (R) correctly explains (A).
Solution:

White and light coloured clothes are poor absorbers of heat, that is why such clothes are preferred in summer. So both the options (A) and (R) are correct, and (R) correctly explains (A).

7. Loss of water from the body through perspiration depends on : [U.P.B.E.O. (Pre) 2019]

Correct Answer: (c) Both (a) and (b)
Solution:

Loss of water from the body through perspiration depends on both atmospheric temperature and atmospheric humidity. Perspiration or sweating allows the body to regulate its temperature.

The rate of sweating depends on many factors and is increased in proportion to the work rate and the environmental temperature and humidity.

8. The most important function of perspiration is to : [R.A.S./R.T.S. (Pre) 1994-95]

Correct Answer: (a) Regulate body temperature.
Solution:

Perspiration is often related to heat. When there is a rise in temperature of the surroundings, the body heats up and that can be dangerous. The temperature of the body has to be stable or else the cells will start to burst.

The problem will occur with the running of the organs and even heat strokes can arise which can lead to death. It is the process of perspiration that cools the body down.

The sweat released onto the body cools it down and when the watery substance evaporates from the skin, it takes the heat with it giving a cooling effect.

9. A fan produces feeling of comfort during hot weather, because - [M.P.P.C.S. (Pre) 2008, 67ᵗʰ B.P.S.C. (Pre) 2022]

Correct Answer: (b) Our perspiration evaporates rapidly
Solution:

In summer, a ceiling fan in the counterclockwise direction can help to cool your home by pushing cool air down. During the hot summer months, though this wind chill effect can work to your advantage by providing a breeze that can help evaporate the skin's moisture quickly, creating a cool feeling.

10. In an earthen pitcher, the water remains cold due to the process of [U.P.P.C.S. (Pre) 2012]

Correct Answer: (b) Evaporation
Solution:

The water remains cold in an earthen pitcher because of evaporation. When liquid changes to a gaseous (or vapour) state without boiling, it is known as evaporation. The earthen pitcher is made of mud and has many minute pores.

It is through these pores that the water, placed inside the pitcher, oozes out. Now to evaporate, the water needs to absorb heat, which will change it to vapour.

The only way the water oozing out of the pitchers can turn to vapour is by absorbing heat from the liquid within the pot. Due to this process of continuous absorption of heat from water inside the pot, in a few hours, this water becomes cool.